Midget variable resistance device



Vlay 30, 1939. c. J. HATHORN 2,160,142

MIDGET VARIABLE RESISTANCE DEVICE Filed April 19, 1957 2 Sheets-Sheet 1 j INVENTOR sgaregced. h aforg W A: RNEY y 1939- ,c. J, HATHORN 2,160,142

MIDGET VARIABLE RESISTANCE DEVICE Filed April 19, 1957 2 Sheets-Sheet 2 INVENTOR C/are/ ce J 70? M'TORNZY Patented Ma an, 1939 PATENT OFFICE y 2,160,142 MIDGET VARIABLE RESISTANCE DEVICE Clarence J. Hathorn St. Marys, Pa., asslgnor to Stackpole Carbon Comp ny, St. Marys, Pa., a corporation of Pennsylvania be of a value from 200 ohms to megohms depending upon the use to which the unit is placed;

16 and the unit may serve as a sensitivity control within an automobile. radio receiving set, and it also may be used as a tone control. Theoutside diameter of my new unit is approximately eleven-sixteenths of an inch, and the overall go thickness of the unit is T approximately one-half inch, which size is considerably smaller than the prior art devices.

Another consideration of the present device is that the shaft should be or substantially the a same size as that used in the larger size tone and volume controls, which means that the shaft diameter should be approximately one-quarter of an inch. The bushing on which the shaft is journaled should also be of the type commonly 39 used in the larger size tone of volume controls in. order that uniform lock washers may be used to hold the unit in position. Hence, the afore: mentioned considerations in a small variable resistance unit may be summarized as: a bushing g5 and shaft of normal size, the base, terminals,

and resistance element of minute size in comparison to the bushing and shaft.

Since the control is of the potentiometer type, there is a definite or fixed circuit and a derived in circuit; hence, three outside electrical terminals should be used.

It is, therefore,'an object of my invention to construct a tone control of the adjustable resistance type wherein the same size of the con- 45 trol shaft and bushing as used in the larger type of tone or volume control is used in this midget size unit.

Another object of my invention is to reduce the number of parts in an adjustable resistance 50 un. t oi the potentiometer type without. reducing thewcorresponding functions. j

Another object of my invention is to provide a metallic casing for the adjustable resistance device with an integrally formed fixed outside I electrical terminal.

Application April 19, 1937, Serial No. 137,653

Q2 Claims. (Cl. 201-55) My invention relates to an adjustable resist- Another object of my invention is to utilize the metallic covering or casing as an electrical conductor of the current from the contact shoe pressure member to one ot'the derived circuit terminals. 5

Another object of my invention is to provide an insulating base which may be partially telescoped by the metallic casing and wherein the base and the casing will be held in a predeter-. mined position by complementary holding and positioning means on each of the elements.

Other objects of my invention are to provide an improved device of the character described of simple and economical construction, and which possesses a maximum amount of serviceability l5 and of strength.

With the above and related objects in view, my invention consists of the details of construction and combination of parts that will hereinafter be fully described when the description is read in conjunction with the accompanying drawings in which:

Fig. 1 is a plan view of an adjustable device of the type embodying my invention. 7

Fig. 2 is a plan view of the rheostat without the casing.

Fig. 3 is a plan view of the base, the terminalsattached to the base, and the resistance element.

Fig. 4 is a sectional view taken on the line l of Fig. 1. 33

Fig. 5 is an exploded view of the various elements constituting the rheostat. Y

Fig. 6 is a perspective view of the assembled base and casing illustrating the positioning and holding means on the base and casing. 35

Fig. '7 is a perspective view of-the unit embody: ing my invention illustrating the position of the outside electrical terminals.

Fig. 8 is a perspective view of .the metallic casing. 40

Referring now in greater detail to the drawings, in Fig. 1 is shown a super midget type of variable resistance device or tone control wherein the overall diameter of the unit is approximately eleven-sixteenths of an inch, and the overall thickness of the unit is approximately one-half of an inch.

A base, generally designated as A, is comprised of insulating material such "as Bakelite. The base A of a disc-like arrangement has a central circular bore ill on which a portion of a rotatable control shaft, generally designated B, revolves.

integrally molded or formed with the base A is ametallic bushing, generally designated as C, 56

"the latter has external threads l2 thereon for journaled on the bores Ill and H. A small anto limit the movementof the member 24 in one dinular extension i5 integrally formed on the oute side of the base A abuts the mounting panel (not shown) to space the electrical conducting elements of the tone control from the mounting panel. The uppersurface l6 of the insulator base is substantially flat and ring-like in order to support a ring-like film type resistance element, generally designated as D. The film-type of conductor is preferably of carbon or a mixture of carbon and a binder, and the resistance element has openings i8 and 20 adjacent its ends for the reception of electrical conducting holding rivets or bolts, the latter will hereinafter be further described.

A small peripheral flange 22 adjacent the outer edge of the ring-like surface It limits the movement of the resistance element D radially outwardly from the base, and an internal flange 23 concentric with the bore iii and adjacent the inner edge of the surface l6 limits the movement of the resistance element D in a direction towards the-center of the base. Hence, in a small unit, of thetype now discussed, the small resistance element Dis adequately supported so that it will not be shifted out of position, particularly since the combined stop and terminal rivet 24 passes through the complementary opening l8 in the resistance element, a complementary opening 26 in the base, and acomplementary opening 25 in an outside terminal 30; and when the outward rection, and from the flange 32 extends a stop portion 33-of the rivet. An electrical conducting rivet or bolt'34 passes through its complementary opening 20 on the resistance element, a complementary opening 38. in the base A, and a complementary opening 38 in one end of another fixed outside terminal 40, and the outside end of the electrical conducting rivet 34 is peened over or expanded to hold the resistance element D, the base A,'and the rivet 34 mechanically and electrically together-hence, the value of the re: sistance between terminals 30 and- 40 is fixed.

Upon the outer curved bounding surface 42 of the base A I show four irregularly spaced radially extending prisms, projections, or aligning members 43, 44, and 43. Each of the prisms is similarly constructed, and each side of each prism is approximately one-half of the thickness of the base and serves to position the combined metallic casing and terminal, generally designated as E. The prisms 43 to 43 position the'casing E I 35 with respect to the base in a direction along the longitudinal axis of the shaft B and in a rotary direction about the longitudinal axis of the shaft. The prisms 44 and 45 on the base are spaced apart so a complementary extension 48 on flange "of the metallic casing E is positioned between them to alignthe cover with respect to the base in a predetermined position and in a rotary dit as'well as, a rectilinear direction along the" ongitudinal axis of the shaft. Also,

50 are folding and positioning lugs s4, 51 which cooperatewith prisms 46 and 43, respectively. The lug 48 has at its end a folding portion 55,

which is adapted to be bent under the base A proof housing, and the casing is prevented from.

totally telescoping the base because of the prisms being engaged by portions of the free edge of the flange 50. If the metallic casing E completely teiescoped the base, then the terminals 30 and 40 would be short circuited, since the terminals 30 and 40 are mounted upon the outside surface of the base.

' The above described structure is essential in order that fixed terminal 52, which is integrally formed with the casing E, will be closely positioned to the terminals 30 and 40 so that when the tone control is assembled in a radio receiving circuit, the person making the electrical connections to the terminals will have the three terminals 30, 40 and 52 closely aligned together in order to facilitate insertion orsoldering of the wire leads to the eyes of the terminals.

The shaft 13 has a groove 56 therein which receives a'split or C washer 58 and the latter abuts against the free end of the bushing C to limit the movement of the. shaft in one axial direction.

The end 60 of the shaft "B which carries the rotatable insulating control head, generally designated as F, has serrations 62 thereon so that the insulator head F will be securely fastened to the shaft, The rotatable ,insulator head is molded directly upon the end of the control shaft B so that no additional fastening-means need be used.

to fasten the insulatort control head F with the shaft B.

The rotatable insulator head F carries the frictionalsliding electrical contact shoe, generally designated as G, and moves the contact shoe'G in selective engagement with the resistance element on the longer arcuate distance separating the terminals 30 and 40. The control head F has- 24 in order to limit the rotary movementof the contact shoe G. In other words, when the surface 81 abuts against the stop extension 33 of the stop pin the rotary movement of the insulator head F is limited in one direction, and when the direction of the shaft is reversed until the surface 88 abuts against the 'pin 24, then the control head is limited in movement the opposite direction. In other words, the longest circumferential distance between the surface 61, 3 taken on the circumference of the insulator head is the arcuate limitation of rotation of the contact shoe G on the resistance element.

The contact shoe G'is comprised of a shaft 1| extending from the free end of the casing flange the shoe G may be pressed engagement'by the combined contact shoe pressure member and frictional sliding contact, generally designated as H. The pressure member His in the shape of an arc of a circle and is mounted on the upper surface 84 of the insulator control head by holding rivets ll, 15 which pass through complementary openings 11, I9. The holding rivet 14 passes through a complementary hole 16 and a complementary opening 11 on the pressure member H and the insulator head F, respectively, and the end of the rivet II is expanded to hold the pressure member and control head rigidly together. The rivet I5, constructed similarly to ,the rivet it, passes through a complementary opening 18 on the pressure member H and an opening I! on the control head F and its end is expanded to hold the control head F together with the pressure head.

It is to. be observed that the openings 11 and 19 in the insulator head F are equally spaced from the opening 12, the latter opening receives the extension 10 of the contact shoe G Hence, it will be readily seen from an inspection of Fig. 4 that the unsupported portion or the pressure member H presses upon the upper end of the contact shoe 0-, and there is flexibility oi the pressure member H between the unsupported point of contact and the points where the pressure member is supported. The free ends and SI construction compared to the prior art devices eliminates at least a fixed or stationary electrical member as well as a fixed terminal fastening member.

A summary of the operation of my invention is as follows:

The impressed or fixed potential diiierence is between the fixed outside-terminals Ill and 40, and the derived circuit or derived voltage may be between the terminal 52 and either terminal 30 or 40. when the tone control is in the electrical circuit, the resistance or impedance drop between one end of the resistance element and the contact shoe is varied by rotating. the control .shai't B, and the control shaft can only be rotated within the limits which is the largest circumferential distance between the control head walls 61 and 58, for either of the walls 61 or I8 may abut against the stop terminal 2 to limit the rotation of the shaft 13 and consequently the contact shoe.

One side of the' derived circuit is termed by the current passing along the resistance element D to whatever position contact D may be thereon, and

cal shape, it is within the scope of my invention to construct the prisms 01' other geometrical shapes so that the same function may be performed. For example, another geometrical shape is a cylindrical stud whose axis may be extending radially with respect to the longitudinal axis of the control shaft.

Although this invention hasbeen described in considerable detail, such description is intended as illustrative rather than limiting, as the inven- 'cept as far as it is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. An adjustable resistance device comprising an. insulating base, a resistance element mounted upon said base, an electric conducting contact shoe for irictionally engaging said resistance element, said contact shoe having a disc-like head in engagement with said resistance element and a cylindrical-like shaft, a rotatably mounted control shaft, an insulating control head having an opening to complementary receive the shaft of the contact shoe, a combined contact shoe pressure member and spring-like electrical contact member, a metallic casing, said combined shoe pressure member engaging the upper end of said contact shoe shaft whereby the contact shoe will be pressed into engagement with the resistance element, and the spring-like electrical contact member being adapted to electrically engage said casing, a peripheral notch on the underside of said insulating control head, a combined rivet holding member and stop member, an outside electrical terminal, said combined member holding one end of'the resistance element and the outside terminal tothe insulating base, said notch in the insulating head being of an arcuate length equal to the angular movement of the control head, the

end wails partially defining the notch on said control head being adapted to abut against the telescoped upon said insulator base.

2.-An adjustable resistance device comprising an insulating base, a resistance element mounted thereon, an electric. conducting contact shoe for frictionally engaging said element and having a shank terminating in a button-like head, a rotatably mounted control shaft, an insulating control head having an opening therethrough ior slidably receiving the shank of the shoe, a metallic casing, a metallic resilient member mounted on said control head and en ging the upper end of the contact shoe shank to bias its button-like head against the resistance element, said resilient member also slidably engaging said casing, an outside electrical terminal, a combined rivetholding member and stop member holding one end oi the resistance element and said terminal to said insulating base and electrically connecting the terminal to the element, said control head being provided with means for engagi said stop member to limit the rotation of the head, and said metallic casing being provided with an outside terminal.

' CLARENCE J. HATHORN. 

